Night at the Reef

Night Dive (or snorkel) is probably the most exciting event of the week!  There are always students that are a little fearful of this activity.  They always have a new sense of confidence by the end of the night.  These are some of the things you will see.

Night Snorkel list   

Playfull Squid , Octopus, sleeping Parrotfish, Basket Star, Lobster, Giant Mithrax, Coral Crab, Cardinal Fish, Green Moray Eel, Portunid Crab, Web Burfish, Baloonfish, light swarming Redear Sardine, light attracted Needle Fish, feeding coral polyps, seasonal bioluminescent Thread Worms, seasonal bioluminescent ostracods, nocturnal color pattern changes (e.g. Blue Tang), nocturnal behavior changes (e.g. Grunt schooling),

Common Name: Caribbean Reef Squid

Scientific Name: Sepioteuthis sepioidea

The most commonly sighted squid in the Caribbean, the reef squid is commonly seen hovering over reefs and turtle grass beds. Reef squid range between 6 in. and 12 in. in length and often remain a safe distance from the surface to avoid predation by birds. Individuals can rapidly change colors and have been shown to communicate by rapidly changing color, shape and texture. Reef squid are generally wary and retreat if threatened or approached rapidly. Here at TREC, if squid are encountered during a snorkel, two methods are employed to keep them close. During the day, the group forms a circle around the squid, trapping the individual such that everyone can see and observe. At night, squid can actually be put into a trance by shining an underwater flashlight on them, thus rendering them fairly immobile and curious.

Common Name: Caribbean Reef Octopus

Scientific Name: Octopus briareus

The Caribbean reef octopus is only encountered at night and is never seen during the day. It inhabits recesses and cavities within the reef during the day and leaves the safety of its lair at night to feed. Individuals are easily identified as they are pale to intense iridescent blue/green in color and typically spread out their limbs over the substrate they are on. The reef octopus feeds on crabs, shrimp, lobster and occasionally fish. Burrows can often be identified by the pile of crab carapaces at the entrance. Individuals are not social and live a solitary life. Here at TREC, the reef octopus is commonly seen during the night snorkel and is often picked up and observed by the group, giving everyone a chance to feel its suckers.

Common Name: Common Octopus

Scientific Name: Octopus vulgaris

This species is the only octopus that may be encountered during the day snorkels and inhabit reefs, rubble, and sea grass beds. A master of camouflage, the common octopus can change body color, texture, and shape to blend in with its surroundings and avoid potential predators. Like the reef octopus, lairs can be spotted by the pile of shells and debris at the entrance. Individuals use their powerful beaks to punch a hole in the shell of their prey before sucking out the fleshy contents.


During the night snorkel, a number of bioluminescent creatures can be observed. The most common are tiny bioluminescent dinoflagellates, which emit bright blue flashes in response to movement. They are brightest after several hours of darkness and glow only at night. During the night snorkel, they can be stirred simply by treading water while flashlights are off, and tiny blue flashes can be seen surrounding group members. Another bioluminescent critter commonly seen in the Caribbean is the threadworm, Odontosyllis enopla. Observed as a glowing halo near the surface, the glow is actually a cloud of bioluminescent mucus release by the female to attract males. The female can often be observed at the center of the cloud, visible as a tiny, glowing crescent. Lastly, bioluminescent ostracods can be spotted occasionally attached to rocks or the reef with their sequenced glow patterns. Males attach to the hard surface and in flashing, attract females to mate with.